Observations

Description

Valves are rhombic-lanceolate and somewhat gibbous at the center, with acutely rounded apices. Pseudosepta are very prominent at the apices. The axial area is narrow near the valve apices, becoming much wider toward the central area. The central area is a wide stauros, expanding in deltoid fashion toward the valve margins. External raphe fissures are lateral, becoming filiform at the distal and proximal ends. Proximal raphe ends are weakly expanded and nearly straight. Striae are strongly radiate throughout and continue onto the valve mantle. Areolae are coarse, 12-15 in 10 µm. Cells are commonly found adherent face-to-face in short colonies. Elements of the cingulum and pseudosepta are evident in girdle view.

Stauroneis acuta has large rhombic-lanceolate valves with a gibbous central region, acutely rounded apices with pseudosepta, straight and weakly expanded proximal raphe ends, strongly radiate striae, and a large stauros shaped like a bow tie.

Compare

The rhombic-lanceolate valves, acutely rounded apices, and straight, weakly expanded proximal raphe ends make S. acuta distinctly different from most other large Stauroneis species with pseudosepta. Stauroneis terryi attains a much larger size and has a wider raphe and axial area.

Stauroneis terryi

Ward

Citations

Bahls, L. (2010).Stauroneis in the Northern Rockies: 50 species of Stauroneis sensu stricto from western Montana, northern Idaho, northeastern Washington and southwestern Alberta, including 16 species described as new.
Northwest Diatoms, Volume 4. The Montana Diatom Collection, Helena, 172 pp.

Patrick, R.M. and Reimer, C.W. (1966).The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1.
Monographs of the Academy of Natural Sciences of Philadelphia 13.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

NCBI Genbank Taxonomy

North American Diatom Ecological Database (NADED)

NADED ID: 62036

Autecology Discussion

Stauroneis acuta is one of two Stauroneis species in the Northern Rockies with frustules commonly found adherent face-to-face in coloneis. The other colony-forming species is Stauroneis kishinena. Stauroneis acuta is widely distributed in small lakes in both the northern and southern hemispheres (Patrick & Reimer 1966, Van de Vijver et al. 2004) and appears to prefer slightly alkaline waters with low to moderate levels of dissolved solids. It is rarely found in large numbers.